In the field of bipolar transistors, energetically developed are heterojunction bipolar transistors (HBTs) in which materials different in bandwidth are introduced to base layers using epitaxial growth to increase device speed. HBT with base layers using family-IV semiconductor materials such as SiGe (silicon-germanium) material and SiGeC (silicon-germanium carbon) material is highly expected as a high-speed device because the device can be formed on a Si substrate and integration with CMOS circuits and large substrate are advantageous in terms of high performance and low cost.
A typical configuration example of a conventional HBT using SiGe for heterojunction (hereinafter referred as to SiGe HBT) is explained with reference to FIG. 23. While the HBT using SiGe material for base layers is exemplified here, a HBT using SiGeC material for the base layers is to have the same configuration.
The SiGe HBT is generally classified into a double-polysilicon structure and a single-polysilicon structure. FIG. 23(a) is a typical schematic sectional view of the SiGe HBT of the double-polysilicon structure and FIG. 23(b) is that of the SiGe HBT of the single-polysilicon structure.
First, the SiGe HBT of double-polysilicon is explained with reference to FIG. 23(a).
A polysilicon layer 103 corresponding to an extrinsic base region is formed in advance on a Si substrate provided with an isolation area 101 and a collector region 102. And the polysilicon layer 103 is subject to a patterning treatment by etching. An epitaxial SiGe layer 104 corresponding to an intrinsic base region selectively and epitaxially grows on an HBT formation region removed the polysilicon layer 103.
In this configuration, the polysilicon layer 103 and the epitaxial SiGe layer 104 can not be formed simultaneously or continuously. Therefore, it is difficult to avoid native oxide film formed on an interface 105 between the epitaxial SiGe layer 104 and the polysilicon layer 103. Also, there is a possibility of generating void inside the interface 105. Thereby, the SiGeHBT of the double-polysilicon structure increases contact resistance between the polysilicon layer 103 and the epitaxial SiGe layer 104 and it causes a problem that uneven contact resistance exists among products. And it has further problems that manufacturing process is complicated and process window is small during selective growth. From these viewpoints, the SiGeHBT of the double-polysilicon structure is not suitable for mass production.
Next, the SiGeHBT of the single-polysilicon structure is explained with reference to FIG. 23(b).
Using a non-selective growth method, an epitaxial SiGe layer 106 corresponding to the intrinsic base region epitaxially grows on the Si substrate directly above the collector region 102. Simultaneously, a polySiGe layer 107 corresponding to an extrinsic base region epitaxially grows on an isolation region 101. And then a silicide layer 108 is formed on a surface of the polySiGe layer 107.
Because this structure enables the PolySiGe layer 107 and the epitaxial SiGe 106 to form simultaneously, neither native oxide film nor void is formed on the interface between epitaxial SiGe layer 107 and polySiGe layer 106. Therefore, increase of contact resistance between both layers is fundamentally solved. And the manufacturing process of the SiGe HBT of the single polysilicon structure is simpler than that of the double-polysilicon structure. Further the process window of the non-selective growth is larger than that of selective growth.
Thus, the SiGeHBT of the single-polysilicon structure is suitable for mass production.
International Publication WO01/88994 is a public-known material to disclose SiGeHBT technology.